Bagworms: How to Spot the Bags and Save Your Evergreens

The evergreen bagworm, Thyridopteryx ephemeraeformis, is a native pest mainly of the eastern US with one generation a year. That explains how to manage it: a long, easy window when the next generation sits in bags you can reach, and a short one when sprays work at all.

What to do with bagworms, month by month

Compiled by The Pest Control Brief from University of Maryland Extension, University of Nebraska NebGuide G1951, Purdue E-27-W, Ohio State HYG-2149, Missouri Botanical Garden and UF/IFAS EENY-548. Hatch runs from mid-May in Georgia to early June in Virginia; see the state table below.

How to identify bagworms

The bag is the giveaway. It is spindle-shaped, made of tough silk studded with bits of needles, leaves and twigs from the host plant, and it hangs from a twig like a small brown Christmas ornament. Finished bags are about 1 to 2 inches (Missouri Botanical Garden) or 1.5 to 2.5 inches (Ohio State).

The caterpillar rarely leaves its bag. When feeding, it pushes its head and front legs out of the top; Virginia Tech describes the front part as mottled brown and cream, and the rest as greyish brown. Disturb it and it pulls back inside and holds the opening shut.

Bagworms or something else?

Fall webworms and eastern tent caterpillars are often called bagworms, but Arizona Extension points out the difference: those species spin large, translucent webs holding many caterpillars, while each bagworm lives alone in an opaque, leaf-covered case. Ohio State describes a separate grass bagworm that makes one-inch bags and attaches them to fences and walls; it does no damage to turf (our lawn pest control guide covers the insects that do). Evergreen bagworms also turn up on fences, decks and siding when they wander off to pupate, Virginia Tech notes.

Do bagworms turn into moths or butterflies?

Moths. Bagworms belong to the moth family Psychidae, about 1,000 species worldwide according to UF/IFAS, in which every larva builds a bag and most adult females cannot fly. In the evergreen bagworm the two sexes look nothing alike. The male is a small moth with a black, furry body, feathery antennae and almost transparent wings spanning about an inch, according to Missouri Botanical Garden. The female never becomes a recognisable moth: she is a soft, yellowish-white, maggot-like adult with no wings, functional legs or antennae, and she never leaves her bag.

Neither adult feeds. The male lives only one to two days and the female a couple of weeks, according to UF/IFAS. After mating she lays 500 to 1,000 eggs inside the bag and dies. Maryland gives a wider range of 200 to 1,000.

Because females cannot fly and larvae move only a few metres from their mother’s host (UF/IFAS), infestations build on the same plant year after year. Young caterpillars do balloon on silk threads in spring, so a clean shrub can be colonised from a neighbour’s.

Are bagworms harmful to humans?

No. None of the extension fact sheets we read lists the evergreen bagworm as biting, stinging, venomous or poisonous. The caterpillars chew foliage, almost never leave the bag and retreat inside when touched; the adults do not feed at all. The hazards extension sheets warn about are to plants, and to people only from the insecticides used against them. Bt, the usual biological spray, is described by Maryland and Georgia extension as not affecting humans or animals.

Do bagworms bite?

We found no extension or medical source describing bagworm bites. Gloves simply make hand-picking easier, because the silk is tough.

Is bagworm harmful? What they do to trees

To plants, yes. Missouri Botanical Garden counts more than 128 host species. Arborvitae, red cedar and other junipers are favourites; spruce, pine, Leyland cypress and many deciduous trees are also eaten.

First damage is easy to miss: tiny caterpillars etch needles, browning branch tips (Nebraska). Maryland warns bagworms often go unnoticed until August, after severe damage, and Arkansas notes stripping is worst near the top. The threshold is low: UF/IFAS cites research finding that as few as four bagworm larvae can make a four-foot arborvitae unmarketable.

Do bagworms kill trees?

They can kill evergreens, and rarely threaten deciduous trees, because conifer foliage that is destroyed “is not regenerated,” as Nebraska puts it, while deciduous plants grow new leaves. Ohio State adds that crowded larvae eat the buds of arborvitae, cedar and juniper, causing branch dieback and open dead patches, and that heavy defoliation “may cause entire plant death during the following season.”

There is a slower kind of damage too. Before pupating, each caterpillar wraps a band of silk around its twig that does not decay quickly; as the twig grows the band can girdle it, killing branches several years later (Ohio State) and leaving a gall-like swelling (Virginia Tech). Cut the band off whenever you remove a bag.

Compiled by The Pest Control Brief from Nebraska G1951, Ohio State HYG-2149, University of Maryland Extension, Virginia Tech ENTO-624 and UF/IFAS EENY-548.

Will a tree recover from bagworms?

A deciduous tree usually will: Nebraska and UConn note deciduous trees regrow leaves, and Virginia Tech says completely defoliated trees usually make a full recovery the next spring if otherwise healthy. Evergreens are the exception. Maryland calls the damage to needled evergreens “cumulative and permanent,” and Ohio State draws the line at severity: moderate defoliation is unsightly, excessive defoliation can kill. Virginia Tech notes heavily infested plants with sparse brown foliage may be better removed than treated.

Where bagworms are found: what the iNaturalist records show

Ohio State gives the range as New England to Nebraska and south through Texas. Our analysis of 14,205 US research-grade iNaturalist records puts the densest sightings on the western edge of that range.

Oklahoma leads at 15.57 records per 10,000 iNaturalist observations, ahead of Kansas at 13.32 and Nebraska at 6.98. Texas, with the most records of any state at 1,759, ranks lower at 1.59 because it records so much else. Florida sits at 0.15, consistent with UF/IFAS calling it an occasional pest there because many host plants grow poorly below zone 8A, and there are no records from California.

The seasonal pattern tracks the bag, not the feeding. Bagworm records are least common relative to everything else in May and June (index 49 and 40), when new bags are tiny and hard to spot, and peak in August and September (141 and 138), when bags are full size and damage is obvious. They stay above average from December to March, most likely because brown bags stand out on winter branches when little else is being recorded. That is exactly the season to remove them.

How do I permanently get rid of bagworms?

No method is permanent, because caterpillars can balloon in from nearby plants, but clearing a plant thoroughly knocks its population right down. Arkansas extension recommends an annual survey in autumn, winter or early spring. This sequence follows the integrated pest management approach.

1. Pick bags from autumn to early spring. Missouri Botanical Garden and Arkansas call it the cheapest control. Finish before eggs hatch in mid-May to early June. Look high: Nebraska notes bags holding males tend to hang lower, so the egg-filled female bags are often higher up.
2. Cut, do not pull. Snip the bag off with scissors or a knife and remove the silk band around the twig so it cannot girdle it later.
3. Destroy the bags. Crush them, drop them in soapy water, or seal them in a bag for the trash. Do not leave them on the ground: Arkansas and Nebraska both warn eggs in discarded bags will hatch and the larvae can climb back. Arizona suggests a jar with coarse screening, so parasitic wasps inside can escape.
4. Encourage natural enemies. At least 11 species of parasitic wasp attack the evergreen bagworm, according to UF/IFAS, and research cited by Georgia and Nebraska extension found that flowering plants near infested shrubs increase parasitism.
5. Spray only young caterpillars, and only if needed. Bt (Bacillus thuringiensis var. kurstaki) works only when eaten, so cover all foliage. Purdue says Bt is effective only on bags under 1 inch long and that larvae may need to feed for one to two days to get a lethal dose; Nebraska advises spraying when bags are under 1/2 inch. Spinosad, neem (azadirachtin) and insecticidal soap are also effective on young larvae, Nebraska says, with minimal impact on beneficial insects. See our neem oil guide.
6. Check two weeks later. Purdue advises looking for live bagworms two weeks after any application to decide whether a second treatment is needed.

Pyrethroids knock down larvae quickly, Ohio State says, but Purdue recommends biorational products first because they spare the natural enemies of spider mites and scale insects. Ohio State also notes mature larvae may pupate early when they detect pesticide, so a late spray can look like it worked when it did not.

Tall trees are where DIY ends: sprays must cover the whole canopy, and Purdue lists soil-applied systemics as commercial products. For a large spruce or a long row of arborvitae, a licensed arborist or certified applicator is the sensible call. Our guide to garden pest control explains how pesticide labels limit what can be sprayed on garden plants and what to ask before hiring.

When exactly to spray: what each extension service says

Egg hatch follows temperature, so the right week depends on where you live. The USA National Phenology Network forecasts caterpillar emergence at 600 to 900 growing degree days above 50°F; Ohio State gives a more precise model and advises allowing an extra week of ballooning after the last emergence before spraying.

Compiled by The Pest Control Brief from the extension publications named. Always use a product whose label lists both bagworms and the plant you are treating.

Should I kill bagworms?

On small evergreens, yes, and early. On a large, healthy deciduous tree, often not: Missouri Botanical Garden notes predators usually control light infestations there, and if the problem does not worsen, spraying is not needed. Arizona extension, where the species is rare, calls them “simply an interesting member of the local ecosystem.”

Frequently asked questions

Is bagworm harmful?

To evergreens, yes; to people, no. Bagworm caterpillars can defoliate arborvitae, juniper, cedar, spruce and pine, and because conifers cannot regrow lost needles, heavy feeding can kill them the following season. Deciduous trees usually regrow their leaves. None of the extension sources we read describes bagworms as biting, stinging or venomous; they are caterpillars that stay inside their bags and eat foliage.

How do I permanently get rid of bagworms?

Pick every bag you can reach between autumn and mid-May, cut away the silk band, and destroy the bags rather than dropping them, since eggs inside can still hatch. Repeat each winter, because young caterpillars can balloon in from neighbouring plants. If there are too many bags, spray a labelled product such as Bt in June while bags are still small, then check again two weeks later.

Should I kill bagworms?

On small evergreens such as arborvitae and juniper, yes: UF/IFAS cites research showing as few as four caterpillars can ruin the look of a four-foot arborvitae, and lost needles are not replaced. On large, healthy deciduous trees, a few bags can usually be tolerated, and Missouri Botanical Garden says spraying is unnecessary if the infestation is not getting worse.

Will a tree recover from bagworms?

Deciduous trees usually do, regrowing leaves the next spring if otherwise healthy, according to Virginia Tech, Nebraska and UConn. Evergreens are different: Maryland extension describes the damage to conifers as cumulative and permanent, because destroyed needles are not regenerated. Moderate defoliation is mainly unsightly, Ohio State says, but heavily defoliated arborvitae, cedar and juniper can die the following season.

Sources

• University of Maryland Extension, Bagworms on Trees and Shrubs, revised 2020.
• Baxendale and Kalisch, Bagworms, University of Nebraska Lincoln Extension NebGuide G1951, 2009.
• Shetlar, Bagworm and Its Control, Ohio State University Extension HYG-2149, 2011.
• Sadof, Bagworms, Purdue Extension E-27-W, 2017.
• Dellinger and Day, Bagworms in Virginia, Virginia Cooperative Extension ENTO-624, revised 2025.
• Moffis and Arthurs, Bagworm, Thyridopteryx ephemeraeformis, UF/IFAS Featured Creatures EENY-548 (IN981).
• Joseph, Bagworms in Urban Landscapes, University of Georgia Cooperative Extension Circular 1237, reviewed 2026.
• University of Arkansas Cooperative Extension Service, Bagworms in Arkansas.
• University of Connecticut Home and Garden Education Center, Bagworm Moth.
• University of Arizona Cooperative Extension, Backyard Gardener 51: Bagworms, 2023.
• Missouri Botanical Garden, Bagworms, updated 2024.
• USA National Phenology Network, Bagworm Pheno Forecast.
• The Pest Control Brief analysis of iNaturalist research-grade records, pulled October 2026.